Method and apparatus for choosing a modulation and coding rate in a multi-user, mimo communication system

ABSTRACT

A method and apparatus for choosing a modulation and coding rate in a MU-MIMO communication system is provided herein. During operation, a node will determine the MCR to feed back to the base even though the mobile does not know which of the possible interferers (if any) will be using the same time/frequency resources as the mobile. This takes place via the mobile node calculating best antenna weights (codebook choice) for each group of subcarriers that can be potentially used by the mobile. Transmit weights v for each interferer are then determined and the weights are utilized to determine a best modulation and coding rate for the mobile.

FIELD OF THE INVENTION

The present invention relates generally to determining a modulation andcoding rate within a communication system, and in particular, to amethod and apparatus for choosing a modulation and coding rate in amulti-user MIMO communication system.

BACKGROUND OF THE INVENTION

Downlink multi-user multiple-input, multiple output (MU-MIMO), alsoknown as transmit spatial division multiple access (Tx-SDMA), is amethod that enables multiple mobiles to share the same time-frequencyresource through downlink beamforming using an antenna array at thebase. This is illustrated in FIG. 1. As shown in FIG. 1, MU-MIMOtransmit beamforming increases the system-level capacity by transmittingto two mobiles on the same time-frequency resource by creating twotransmit beams patterns 101 and 103. Transmit beam pattern 103 maximizesthe power to mobile 1 and transmits little power toward mobile 2 whereastransmit beam pattern 101 maximizes the power to mobile 2 and transmitslittle power toward mobile 1. This type of beamforming is accomplishedby employing multiple antennas 102 at the transmit site and weightingeach antenna such that the combined transmissions result in a beamformedpattern that enables two data streams to be transmitted on the sametime-frequency resource where one data stream is destined for mobile 1and the other data stream is destined for mobile 2.

To enable downlink MU-MIMO, channel information for multiple users isneeded at the base station. In time division duplexing (TDD) systemswhere the uplink and downlink use the same carrier frequency, thechannel information is easily obtained by the mobile sounding the uplinkand exploiting channel reciprocity. However, in frequency divisionduplexing (FDD) where the uplink and downlink are on different carrierfrequencies, the channel information cannot be obtained with uplinksounding and thus the mobiles have to use some sort of feedbackmechanism in order to provide channel information to the base. Onemethod of obtaining this feedback is codebook feedback which is known inthe art. In codebook feedback, the base station and the mobiles all usea same codebook which is a collection of B vectors or matrices. A mobilewill measure the downlink channel from all base station antennas andthen will choose the best codebook vector or matrix that matches thedownlink channel. The mobile will feed back this best codebook choice tothe base station which can then use this selection to determine thetransmit weights on the downlink.

In addition to beamforming, many communication systems may utilizemultiple Modulation and Coding rates (MCRs). Particularly, the MCR of atransmitted data stream for a particular receiver can be tailored topredominantly match a current received signal quality (at the receiver)for the particular frame being transmitted. The MCR may change on aframe-by-frame basis in order to track the channel quality variationsthat occur in mobile communication systems (this method of choosing theMCR is called adaptive modulation and coding). Thus, streams with highquality are typically assigned higher order modulations rates and/orhigher channel coding rates with the modulation order and/or the coderate decreasing as quality decreases. For those receivers experiencinghigh quality, modulation schemes such as 16 QAM or 64 QAM are utilized,while for those experiencing low quality, modulation schemes such asBPSK or QPSK are utilized. Multiple coding rates may be available foreach modulation scheme to provide finer MCR granularity, to enable acloser match between the quality and the transmitted signalcharacteristics (e.g., coding rates of ¼, ½, and ¾ for QPSK; and codingrates of ½ and ⅔ for 16 QAM, etc.).

Besides choosing the best codebook index, the mobile needs to alsoselect the best MCR which is typically fed back in a channel qualityindication (CQI) message. Because MU-MIMO has multiple users sharing thesame time/frequency resource, it may be difficult for a mobile to knowits channel quality prior to users being assigned their time/frequencyresource. In other words, because a mobile will not know its possibleinterferers (i.e., those using the same time/frequency resource), it isdifficult for a mobile to determine an MCR that will match the channelquality when all mobiles are assigned their resources. Therefore a needexists for a method and apparatus for choosing a modulation and codingrate in a MU-MIMO communication system that alleviates theabove-mentioned difficulties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a MU-MIMO communication system.

FIG. 2. is a block diagram of a node in a MU-MIMO communication system.

FIG. 3. is a flow chart showing operation of the node of FIG. 2.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions and/or relative positioningof some of the elements in the figures may be exaggerated relative toother elements to help to improve understanding of various embodimentsof the present invention. Also, common but well-understood elements thatare useful or necessary in a commercially feasible embodiment are oftennot depicted in order to facilitate a less obstructed view of thesevarious embodiments of the present invention. It will further beappreciated that certain actions and/or steps may be described ordepicted in a particular order of occurrence while those skilled in theart will understand that such specificity with respect to sequence isnot actually required. It will also be understood that the terms andexpressions used herein have the ordinary technical meaning as isaccorded to such terms and expressions by persons skilled in thetechnical field as set forth above except where different specificmeanings have otherwise been set forth herein.

DETAILED DESCRIPTION OF THE DRAWINGS

In order to alleviate the above-mentioned need, a method and apparatusfor choosing a modulation and coding rate (MCR) in a MU-MIMOcommunication system is provided herein. During operation, a node willdetermine the MCR to feed back to the base even though the mobile doesnot know which of the possible interferers (if any) will be using thesame time/frequency resources as the mobile. This takes place via themobile node calculating a best codebook choice for each group ofsubcarriers that can be potentially used by the mobile. Next transmitweights v for each possible interferer given the codebook selection arethen determined and the weights are utilized to determine a bestmodulation and coding rate for the mobile.

The above-described procedure allows mobile units to determine amodulation and coding rate for each resource prior to being assigned aresource and MU-MIMO interferer by the base station.

The present invention encompasses a method for a mobile to determine abest modulation and coding rate for a resource within a communicationsystem employing adaptive modulation and coding and transmit spatialdivision multiple access. The method comprises the steps of determininga codebook choice for the resource, determining one or more possibleinterferers, determining antenna weights for the mobile, and determiningantenna weights for the possible interferers based on the codebookchoice. The antenna weights for one or more possible interferers and theantenna weights for the mobile are used to determine a modulation andcoding rate for the mobile.

The present invention additionally comprises a mobile to determine abest modulation and coding rate for a resource within a communicationsystem employing adaptive modulation and coding and transmit spatialdivision multiple access. The mobile performs the steps of determining acodebook choice for the resource, determining one or more possibleinterferers, determining antenna weights for the mobile, and determiningantenna weights for the possible interferers based on the codebookchoice. The antenna weights for one or more possible interferers and theantenna weights for the mobile are used to determine a modulation andcoding rate for the mobile.

Finally, the present invention encompasses a mobile to determine a bestmodulation and coding rate for a resource within a communication systememploying adaptive modulation and coding and transmit spatial divisionmultiple access. The mobile comprises a database and logic circuitrydetermining a codebook choice for the resource, determining one or morepossible interferers, determining antenna weights for the mobile,determining antenna weights for the possible interferers from thedatabase and based on the codebook choice, and using the antenna weightsfor one or more possible interferers and the antenna weights for themobile to determine a modulation and coding rate for the mobile.

For the following text, it will be assumed that only a single datastream is to be sent to each mobile. Also an orthogonal frequencydivision multiplexing (OFDM) system will be assumed where k indicatesthe subcarrier and b the OFDM symbol number. Let there be N_(u) MU-MIMOusers to be transmitted to, M_(T) antennas at the transmitter (base),and M_(R) antennas at the receiver (mobile). The received M_(R)×1 signalat mobile m is given as:

$\begin{matrix}{{Y_{m}\left( {k,b} \right)} = {{{H_{m}\left( {k,b} \right)}{\sum\limits_{u = 1}^{N_{u}}\; {{v_{u}(k)}{x_{u}\left( {k,b} \right)}}}} + {N_{m}\left( {k,b} \right)}}} & (1)\end{matrix}$

where M_(R)×M_(T) H_(m)(k,b) is mobile m's channel, v_(u)(k) is theM_(T)×1 MU-MIMO weight for mobile u (v_(u)(k) is assumed not to changein time over a transmitted frame but may change from frame to frame),x_(u)(k,b) is mobile u's data, and N_(m)(k,b) is additive noise withcovariance matrix σ_(m) ²I where I_(m) is an m×m identity matrix andσ_(m) ² is the noise power on each receive antenna. Note that v_(u)(k)in general can change across frequency but in many cases will be fixedover some number of subcarriers. Thus for simplicity, v_(u)(k) will beassumed to be fixed (constant) over groups (or clusters) of Ksubcarriers so that only one codebook index will need to be fed back foreach group of K subcarriers. Also note that only a single data stream(x_(u)(k,b)) is transmitted to each mobile. However it isstraightforward to extend this description to the case where there aremultiple data streams sent to each mobile.

The MU-MIMO method described above will require only a rank 1 (i.e.,vector) codebook and in general will follow prior-art proceduresdescribed in B. Mondal, et. al., “An Algorithm for 2-User Downlink SDMABeamforming with Limited Feedback for MIMO-OFDM Systems,” in Proc.ICASSP 2007, Honolulu, Hi., Apr. 15-20, 2007, for designing the MU-MIMOweights.

The use of just vector-based feedback as opposed to matrix feedbacksimplifies the computation and also enables the use of the same codebookindex selection for rank-1 SU-MIMO and MU-MIMO. However, the use ofvector codebook is not limiting and a matrix codebook could also be usedwith the following CQI mechanism. To simplify the description, assumethat there are only N_(u)=2 mobiles to be paired for MU-MIMOtransmission (i.e., the mobile and the MU-MIMO interferer) and thatthere are B codebook vectors denoted c₁ through c_(B). Any well designedcodebook as is known in the art can be used.

MU-MIMO Weight Calculation

Given a set of transmit MU-MIMO weights for each codebook vector, a CQImethod is then utilized to determine a modulation and coding rate whichis fed back to the base. The CQI method described below is not limitedto the exact transmit weights, but for simplicity two options forcomputing the set of transmit MU-MIMO weights are considered which arezero forcing with regularization and subspace averaging as are known inthe art. Assume that one mobile chooses codebook vector c_(m) and themobile which will get paired with that mobile chooses codebook vectorc_(n). For the two given codebook vectors, c_(m) and c_(n), thezero-forcing weights, v_(m,n), are given by (v_(m,n) is the MU-MIMOweight used for the mobile that selected index m when n is the indexchosen by the other mobile):

v _(m,n)=((c _(m) c _(m) ^(H) +c _(n) c _(n) ^(H) +αI _(M) _(T) )⁻¹ c_(m))*   (2)

where * indicates conjugation and α is the regularization factor whichcontrols the depth of the null steered. For example, α=0 would steer aperfect null in the direction of c_(n) (true zero forcing) whereas ahigher α steers more energy in the direction of c_(m) and less of a nullin the direction of c_(n). The regularization factor is a good featuresince a perfect null can only be steered toward a mobile only when c_(n)is exactly matched to its channel over all subcarriers in the dataallocation and the channel does not change from the time it is measuredand the time that the MU-MIMO weights are applied. The regularizationfactor is also good because each mobile likely can tolerate a level ofcrosstalk as long as the crosstalk is less than the noise power seen bythe mobile.

The second option for computing the MU-MIMO weights uses a subspaceaveraging to tradeoff the null depth and signal power. These weights arecomputed as follows:

V _(m,n)=(avg(c _(m,) P _(n) c _(m)))*   (3)

where avg(a,b) is the dominant eigenvector of aa^(H)+bb^(H) andM_(T)×M_(T) P_(n) is given as:

$\begin{matrix}{P_{n} = {I_{M_{T}} - \frac{c_{n}c_{n}^{H}}{c_{n}^{H}c_{n}}}} & (4)\end{matrix}$

Note that since there are a finite number of codebook vectors, theMU-MIMO weights for either zero forcing or subspace averaging can beprecomputed and stored. Thus the transmit weights could be known byeither end once the determination is made of which mobiles are pairedfor the MU-MIMO transmission.

A third option for MU-MIMO weights is to use directly the codebookvector chosen by the mobile:

V_(m,n)=c_(m).   (5)

In this method a mobile that chose codebook c_(n) is normally onlypaired with the mobile that chose codebook cm if c_(n) is orthogonal toc_(m). Typically not just any two mobiles can be arbitrarily paired fortransmission. In reality if one mobile selects codebook vector c_(m),then it is likely that not all other B−1 codebook vectors are all goodchoices to be paired with c_(m). Thus there is usually a list of N_(p)possible codebook vectors (N_(p)<B) that can be paired with c_(m) andthus a mobile that chooses codebook vector c_(n) would only be pairedwith the mobile who chose c_(m) if c_(n) is in the list of N_(p)possible codebook vector pairings for codebook vector c_(m). The list ofthe N_(p) possible codebook vectors that can be paired with c_(m) isdenoted S_(m) and note that the codebook vectors in S_(m) is a subset ofthe codebook.

Once N_(p) is selected based on the amount of desired feedback andMU-MIMO weight performance, then the set of possible vectors that can bepaired with index n, S_(n), can be found as the N_(p) indices (m) thathave the smallest of the following metric:

∥c_(n)c_(n) ^(H)−P_(m)c_(n)c_(n) ^(H)P_(m)∥_(F)   (6)

where and ∥A∥_(F) is the Frobenius norm (i.e., the square root of thesum of the magnitude of the elements of A). Note that, depending on thecodebook structure there may be a non-zero probability that severalvalues of n, m may result is the same value of the metric in (5) Error!Reference source not found. If just a few pairs need to be selected outthis group of several pairs with the same metric, then any of the pairscan be chosen.

Determine the Best N_(p) Pairs for the Scheduler

The next step is to determine which codebook vector selections should bepaired. As mentioned above the set of N_(p) possible pairs for codebookindex n is denoted S_(n) and it will be assumed that F≧N_(u)=2 mobileswill send feedback on the block of K subcarriers. Note that by makingF>2 will give the scheduler more flexibility in pairing users and willmake it more likely that two mobiles can be paired, but more feedback isrequired with increasing F, N_(p), F and the codebook size, B, willdetermine the probability that two mobiles can be paired on a givengroup of subcarriers. For example if B=16, N_(p)=3, and F=2, then thereis only a 3/16 chance that MU-MIMO can be performed on the subcarriergroup, however if F=5 then there is about a 90% chance that MU-MIMO canbe performed. The choice of N_(p) will also affect how well the MU-MIMOweights will operate. For example if each vector in the codebook hasthree other vectors that are orthogonal to it, then N_(p)=3 gives a goodset of MU-MIMO weights that are orthogonal to the codebook selected bythe other mobile (of course because of quantization error, the MU-MIMOweights will likely not be orthogonal to the other mobile's channel).However more feedback is required (i.e., F needs to be larger) to ensurethat MU-MIMO is used a reasonable percent of the time. If N_(p)=B−1 thenF can equal 2 (thus minimizing the feedback required) and theprobability of being able to use MU-MIMO is (B−1)/B, however the quality(i.e., orthogonality between paired mobiles) can vary quite a bit.

Determination of the Best Codebook Index

Before determining a modulation and coding rate for the group of Ksubcarriers, the mobiles need to determine the index of the bestcodebook vector, denoted l_(m), which may accomplished using thefollowing metric:

$\begin{matrix}\begin{matrix}{l_{m} = {\arg \; \max \left\{ {\sum\limits_{k = 0}^{K - 1}\; {{{H_{m}\left( {k,b} \right)}c_{l}}}_{F}} \right\}}} \\{= {\arg \; \max \; c_{l}^{H}\left\{ {\sum\limits_{k = 0}^{K - 1}\; {{{H_{m}^{H}\left( {k,b} \right)}{H_{m}\left( {k,b} \right)}}}_{F}} \right\} c_{l}}} \\{= {\arg \; \max \; c_{l}^{H}R_{m}c_{l}}}\end{matrix} & (7)\end{matrix}$

where K is the subcarrier group size (i.e., the number of subcarrierswhere the MU-MIMO transmit weight is fixed) and R_(m) is the spatialcorrelation matrix for the subcarrier group which is determined from thedownlink channel estimates.

An alternate method of determining the index of the best codebook vectorover a subcarrier group (i.e., the number of subcarriers where theMU-MIMO transmit weight is fixed) comprises of the following steps:

-   -   1. Determine a set of one or more possible interferers for a        given codebook vector. The set of possible interferers may or        may not comprise of other codebook vectors. The set of possible        interferers may or may not be orthogonal to the given codebook        vector. The set of possible interferers for a given codebook        vector may or may not vary with time or frequency.    -   2. Determine a post-processing signal to inference plus noise        ratio (SINR) for a given codebook vector based on the determined        set of possible interferers. The computation of post-processing        SINR may assume an minimum-mean-squared-error (MMSE) receiver.    -   3. Select the codebook vector with the maximum SINR as the best        codebook vector.        After the choice of the best codebook index and before the        determination of the modulation and coding rate, the mobile may        also determine one or more possible interferers from the set of        possible interferers corresponding to the best codebook index if        post-processing SINRs were determined during the step of the        best codebook vector selection. The mobile has a choice of        several ways of determining possible interferers:    -   1. The interferer corresponding to an SINR closest to the mean        of the SINRs for the possible interferers.    -   2. The interferer corresponding to the maximum or minimum SINR        among the SINRs for the possible interferers.

Determination of the Modulation and Coding Rate (MCR)

Besides choosing the best codebook index, the mobile will need to selectthe best MCR which is typically fed back in a CQI message. Although thecodebook index will be selected on a group of K subcarriers, only oneCQI report is typically sent for the entire bandwidth (N≧K subcarrierswhere usually N>>K). The CQI is one value over the entire band to reducethe feedback and simplify the coding and scheduling operations at thebase. In the preferred embodiment of the present invention the mobiledetermines the MCR to feed back to the base even though the mobile doesnot know which of the N_(p) possible interferers will be present. TheMCR/CQI is determined as follows:

-   -   1. For a group of subcarriers for use by the mobile as a        resource, determine the best codebook choice for antenna        weighting for that group of subcarriers.

As is known in the art, one possible codebook choice maximizes transmitenergy in the direction of the mobile. Additionally, mobiles will knoweach possible interferer based on their codebook choice. Moreparticularly, for a particular codebook vector selected by a mobile (saycodebook vector c_(n) is selected) there will be an associated set ofcodebook vectors (S_(n)) that can be paired with a mobile that made thatcodebook selection. A different mobile that selects codebook vectorc_(m) will be paired with a mobile that selected c_(n) only if c_(m) isan element of S_(n). Therefore the best codebook choice is used todetermine transmit weights and also the set of N_(p) possibleinterferers (i.e., possible mobiles that can be paired with the firstmobile).

-   -   2. Each of the N_(p) possible interferers will have a different        associated codebook vector c_(m). However when the base actually        transmits on the downlink, only one of these interferers (and        associated codebook vector c_(m)) will be selected. But since        each mobile will not know beforehand which mobile they are to be        paired with, the mobile that chose codebook vector c_(n) will        have to first determine the transmit weights for itself and the        interferer (denoted v_(n,m) and v_(m,n) respectively) for each        of the N_(p) possible interferers. Then using these weights, the        mobile can determine the MCR/CQI. Note that the set of weights,        v_(n,m) and v_(m,n), are the one possible set of transmit        weights, denoted by v, that the interferer with associated        codebook vector c_(m) may have if paired with the mobile that        chose codebook vector c_(n).    -   3. For each of the N_(p) possible interferers, compute a        potential receive signal strength from the base station to the        mobile that chose codebook index n as G_(m)        ^({dot over (a)})(k)=Ĥ_(u)(k)v_(n,m). Also compute a crosstalk        (interference) signal from each of the N_(p) interferers as        G^(i) _(m)(k)=Ĥ_(u)(k)v_(m,n) for subcarriers, k, where Ĥ_(u)(k)        is an estimate of the broadcast channel for the mobile. When        completed the mobile that chose codebook index n will have an        estimate of the desired signal, G_(m) ^(d)(k), and the        interfering signal, G_(m) ^(i)(k) for each of the possible        interferers.    -   4. Compute or be provided a noise estimate, σ_(n) ², by        measuring the noise on each subcarrier.    -   5. For each of the possible interferers, compute the        post-reception signal to interference plus noise ratio (SINR) on        each subcarrier in the group of subcarriers as a function of the        desired signal, the interfering signal, and the noise estimate.        For example the post-reception SINR, δ_(m)(k), can be determined        as:

$\begin{matrix}{{\delta_{m}(k)} = \frac{{{G_{m}^{d}(k)}}^{2}}{{{G_{m}^{i}(k)}}^{2} + \sigma_{n}^{2}}} & (8)\end{matrix}$

-   -   6. Determine a single post-reception SINR from the set of        possible SINR values for each interferer. For example, the        interferer, m, that gives the largest average SINR across all K        subcarriers can be chosen (in this case δ(k)=δ_(m)(k)). Another        option is to compute an average SINR over all interferers as

${\overset{\_}{\delta}(k)} = {\frac{1}{N_{p}}{\sum\limits_{m \in S_{n}}\; {{\delta_{m}(k)}.}}}$

Yet another option is to choose the single interferer, m, that gives theaverage SINR over all interferers (in this case δ(k)=δ_(m)(k)).

-   -   7. Use the single post-reception SINR, δ(k), on each subcarrier        to determine a metric which is can be mapped to the best MCR        choice. The choice of MCR based on SINR could be made in one of        several ways. For example, using the known in the art technique,        exponential effective SIR mapping (EESM), which computes the        following effective SINR over the resource from the single        post-reception SINR value on each subcarrier:

$\begin{matrix}{\gamma_{eff} = {{- \beta}\; {\ln \left( {\frac{1}{K}{\sum\limits_{k = 1}^{K}\; ^{{- {\overset{\_}{\delta}{(k)}}}/\beta}}} \right)}}} & (9)\end{matrix}$

where there is a different β for the different MCR levels (i.e., adifferent β for rate ½ QPSK, rate ¾ QPSK, rate ½ 16-QAM, etc.). Ifγ_(eff) is greater than a certain threshold for a MCR (e.g., thethreshold could be the SNR value where the performance of that MCR inGaussian noise gives a certain frame error rate such as 10%), then thatMCR is a possible candidate. The mobile may then select the MCR from thelist of possible candidate MCRs that gives the highest throughput. Ofcourse other methods known in the art can also be used to map the singlepost-reception SINR value to a MCR such as the received bit mutualinformation rate (RBIR) procedure.

FIG. 2 is a block diagram showing mobile node 200. As shown, node 201comprises database 205, logic circuitry 203, receive circuitry 202, andtransmit circuitry 201. Logic circuitry 203 preferably comprises amicroprocessor controller. In the preferred embodiment of the presentinvention logic circuitry 203 serves as means for controlling node 200,and as means for determining an MCR for node 200. Additionallytransmitter 201 and receiver 202 are common circuitry known in the artfor communication utilizing a well known communication protocol. In thisparticular embodiment, transmitter 201 and receiver 202 are designed tooperate utilizing a MU-MIMO communication system protocol. Duringoperation, logic circuitry 203 will determine a best codebook choice forantenna weighting for a particular group of subcarriers, and thendetermine transmit weights for itself and each potential interferer.Using the transmit weights for itself and each potential interferer,logic circuitry 203 will determine an MCR and CQI message.

FIG. 3 is a flow chart showing operation of node 200. More particularly,FIG. 3 shows those steps taken by node 200 when determining a modulationand coding rate. The logic flow begins at step 301 where all possiblegroups of subcarriers that can be utilized as a resource are determinedby logic circuitry 203 and a best codebook choice for each group ofsubcarriers (resource) is determined (step 303). As discussed above, thebest codebook choice provides for maximum transmit energy in thedirection of the mobile 200. Also, with each codebook choice exists apossible set of N_(p) interferers (i.e., other mobiles) that may bepaired with mobile 200, sharing the same set of subcarriers (resources).These one or more possible interferers are determined at step 304 bylogic circuitry 203.

Antenna weights for the mobile are then determined by logic circuitry203 (step 305). As described above in the MU-MIMO Weight Calculationsection, the antenna weights may be based on the possible interferersand the codebook choice, or may simply be based on the codebook choice.

There can only exist one possible set of transmit antenna weights v thateach interferer may have if paired with mobile 200. These weights arestored in database 205, and determined by logic circuitry 203 at step307. The transmit weights (antenna weights) for each interferer choicemaximizes transmit energy in the direction of the interferer whilesteering little energy in the direction of the mobile 200. In steps309-317 the transmit weights of the node and possible interferers areutilized by logic circuitry 203 to determine a best MCR/CQI.

At step 309, logic circuitry 203 calculates a potential receive signalstrength G_(d) and a crosstalk G_(i) for each of the N_(p) interferersfor each potential resource. At step 311 a noise estimate is taken bylogic circuitry 203 instructing receiver 202 to measure the noise ofeach resource group. With the signal strength, crosstalk (interference),and noise known for each of the N_(p) interferers, for each resourcegroup, logic circuitry 203 then calculates a post-reception qualitymetric for each subcarrier in each resource group (step 313). In anembodiment of the present invention, the quality metric comprises anSINR, however other quality metrics may be used (e.g., SNR, capacitymeasure, or signal strength). At step 315, the post-reception qualitymetric is then used to calculate an MCR for each potential resource fromthe resource group. The MCRs are then reported back to the base stationvia transmitter 201 as a CQI message (step 317).

While the invention has been particularly shown and described withreference to a mobile that uses a codebook to select a set of antennaweights for transmission as well as for computing CQI, the invention maybe applied to mobiles that do not use a codebook for selecting antennaweights. Specifically this invention may be applied to mobiles thatemploy channel reciprocity based methods like uplink sounding forsending transmit antenna weight information to the base-station. Thisinvention may also be applied to mobiles that employ analog feedbackbased methods like covariance or Eigen-vector feedback for sendingtransmit antenna weight information to the base-station. In such casesthe mobile may use a codebook specifically for determining CQI but notfor determining transmit antenna weights. It is intended that suchchanges come within the scope of the following claims:

1. A method for a mobile to determine a best modulation and coding ratefor a resource within a communication system employing adaptivemodulation and coding and transmit spatial division multiple access, themethod comprising the steps of: determining a codebook choice for theresource; determining one or more possible interferers; determiningantenna weights for the mobile; determining antenna weights for thepossible interferers based on the codebook choice; and using the antennaweights for one or more possible interferers and the antenna weights forthe mobile to determine a modulation and coding rate for the mobile. 2.The method of claim 1 wherein the antenna weights for the mobilemaximizes transmit energy in the direction of the mobile while steeringa null in the direction of one or more interferers.
 3. The method ofclaim 1 wherein the antenna weights for the possible interferersmaximizes transmit energy in the direction of an interferer whilesteering a null in the direction of the mobile.
 4. The method of claim 1wherein the one or more possible interferers are determined based on thecodebook choice.
 5. The method of claim 1 wherein the antenna weightsfor the mobile and the antenna weights for one or more possibleinterferers comprise base station transmit antenna weights used by thebase station when transmitting information to the mobile and the one ormore interferers.
 6. The method of claim 1 wherein the step ofdetermining antenna weights for possible interferers comprises the stepsof: determining a signal to interference plus noise ratio (SINR) for themobile based on signal strength and interference for different choicesof possible interferers; and selecting antenna weights from the codebookfor the possible interferers based on the determined SINR for themobile.
 7. The method of claim 1 wherein the step of using the antennaweights for one or more possible interferers and the antenna weights forthe mobile to determine a modulation and coding rate for the mobilecomprises the steps of: computing a potential receive signal strengthfor the mobile; computing an interference for one or more possibleinterferers; and determining the modulation and coding rate based on thecomputed receive signal strength and the interference.
 8. The method ofclaim 7 wherein the step of determining the modulation and coding ratecomprises the steps of: determining a signal to interference plus noiseratio (SINR) over all possible interferers based on the signal strengthand the interference for each of the possible interferers; anddetermining the modulation and coding rate based on the average SINRover all possible interferers.
 9. The method of claim 7 wherein the stepof determining the modulation and coding rate comprises the steps of:determininlnposelstartlnposelendg a possible interferer that providesthe highest signal to interference plus noise ratio (SINR) to the mobileover the resource; determining the interference for the interferer thatprovides the highest average SINR; and determining the modulation andcoding rate based on the receive signal strength and the interferencefor the interferer that provides the highest average SINR.
 10. Themethod of claim 7 wherein the step of determining the modulation andcoding rate comprises the steps of: determining a possible interfererthat is closest to the signal to interference plus noise ratio (SINR)over all possible interferers over the resource; determining theinterference for the interferer that is closest to the average SINR overall possible interferers and determining the modulation and coding ratebased on the receive signal strength and the interference for theinterferer that is closest to the average SINR over all possibleinterferers.
 11. The method of claim 7 further comprising the step of:computing a noise estimate for the resource; and wherein the modulationand coding rate is additionally based on the noise estimate.
 12. Themethod of claim 7 further comprising the step of: determining apost-reception signal to interference plus noise ratio (SINR) from thereceive signal strength, the interference for one or more possibleinterferers, and the noise estimate; and wherein the modulation andcoding rate is based on the SINR.
 13. The method of claim 1 furthercomprising the step of: transmitting the modulation and coding rate to abase station in a channel quality indication (CQI) message.
 14. A mobileto determine a best modulation and coding rate for a resource within acommunication system employing adaptive modulation and coding andtransmit spatial division multiple access, the mobile performing thesteps of: determining a codebook choice for the resource; determiningone or more possible interferers; determining antenna weights for themobile; determining antenna weights for the possible interferers basedon the codebook choice; and using the antenna weights for one or morepossible interferers and the antenna weights for the mobile to determinea modulation and coding rate for the mobile.
 15. The mobile of claim 14wherein the antenna weights for the mobile maximizes transmit energy inthe direction of the mobile while steering a null in the direction ofone or more interferers.
 16. The mobile of claim 14 wherein the antennaweights for the possible interferers maximizes transmit energy in thedirection of an interferer while steering a null in the direction of themobile.
 17. The mobile of claim 14 wherein the one or more possibleinterferers are determined based on the codebook choice.
 18. A mobile todetermine a best modulation and coding rate for a resource within acommunication system employing adaptive modulation and coding andtransmit spatial division multiple access, the mobile comprising: adatabase; logic circuitry determining a codebook choice for theresource, determining one or more possible interferers, determiningantenna weights for the mobile, determining antenna weights for thepossible interferers from the database and based on the codebook choice,and using the antenna weights for one or more possible interferers andthe antenna weights for the mobile to determine a modulation and codingrate for the mobile.
 19. The mobile of claim 18 wherein the antennaweights for the mobile maximizes transmit energy in the direction of themobile while steering a null in the direction of one or moreinterferers.
 20. The mobile of claim 18 wherein the antenna weights forthe possible interferers maximizes transmit energy in the direction ofan interferer while steering a null in the direction of the mobile.